The long term of Project 1 is to provide the the scientific basis of age- related changes in auditory behavior (presbyacusis) of human subjects. Whereas most studies of presbyacusis use monaural signals in relatively simple psychophysical tasks, the proposed research uses monaural and binaural signals in both psychophysical and electrophysiologic experiments. The auditory signals and listening tasks are selected to challenge the limits of the auditory system to process auditory information. There are three specific aims. Aim 1.1 is the psychophysical assessment of frequency, intensity, and duration discrimination of the aging, binaural auditory system of human subjects. The experiments included under Aim 1.1 and 1.2 (below) are driven by the hypothesis that age-related deficits in auditory behavior, which are assessed monaurally and which are independent of losses of auditory sensitivity, are magnified when assessed under more rigorous conditions such as in binaural hearing. Aim 1.2 is the electrophysiologic assessment of the aging, binaural auditory system of human subjects. The focus is on electrophysiologic correlates of binaural hearing, and intensity discrimination. Aim 1.3 is the electrophysiologic assessment of the temporal resolving power of the aging auditory system of human subjects. The hypothesis is that decreases in temporal coding in aging subjects are due to abnormal processing in the auditory central nervous system. In addition to describing the basic properties of age-related hearing loss, results of the proposed research should identify and assess age-related effects due to the auditory periphery, age-related effects due to the auditory central nervous system, and interactions between the periphery and the central nervous system. These results will provide improvements in diagnosis, treatment, and management of age-related hearing loss in humans.